Preparation of photographic emulsions



is s

Patented July 2l, Y1953 Umrlao-STA'TESv PATENT o-FFICE PREPARATION oF PHoroGRAPHIo:

' EMULsIoNs Rudolph E.v Damsc/hroder, Rochester, N. Ygas'- signor to Eastman Kodak Company, Rochester, N. Ys, a1 corporation of New Jersey No Drawing.

This invention relates "to methodsv of 'prepar-` ing'l photographic silver' halide emulsions fand more particulary toaprocess oi forming' photographic emulsions wherein by-products are re-v moved yfor example-bymeans ofvacuum.

It is well known in the art of photographic emulsion making 'that itis desirable to removev soluble salts resulting'fromuthe 'emulsion makingreactions especiallyinfthose` caseswhere the emulsion is designed Vfor coatingfon transparent supports; Equally well known arer emulsions of the type where ammonia is used in making the j emulsion and is present'in the reaction mixture after formation of thesilver halide. In such processes the ammonia and any soluble salt present is customarilyjremoved by shredding the emulsion* andwashingfwith water by osmosis.

lInisuchf pro'cessesitgis; customary'in the art,

after precipitation of silver halide inthe presence of' alprotecti've'fcolloid,*to chill the emulsion so that it can bereut' up; and-shredded following whichy thepiecesfare1washed for the desired time to remove salts or Vdissolved materialesuclr as.

ammonia. Frequently-this process requires many hours"to.;.'efEectthearemoval of salt, and is per-A formed inibatches'iin crocksg., tanks, shredding machin'es1-and'otherl equipment-'v for ch1ll1ng, shredding f andjwashing:.theA emulsion.

emulsion as bymeans ofvvacuum'. A, stillffurthenA object .is :top provide ff an-..feconomica1 process:` of., forming aspliotographio: emulsion olif-fA optimum. quali'ty :,z lurtherV` objects Vot ,myinvention willV become :apparent from? consideration ofthe f folj lowing." description. i.

My invention resides and the objects-aref-y accomplished; by). reactionfsof.-y an... aqueous ammomia-car lsolution .off.T a; silver compound with. anammoniumxor;alkyl-ammonium. halideso `that the .reactionsproducts.;include,.silverhalide, and

other.;` materialsmostooiv which" ar-ef completely volatilefw. Ther-reaction ,ofthe` silver compound.. with; thehalideriscarriedt out inthe presence of. 3 a peptizing- Vlyophilic colloid,: ef: g. gela-tins.y

' It will be apparent that whengwuseyacuum.

,for rernoval4 .off.afvolatile material .dissolved iin a :reaction mixture, a- VCITY `economical, process .is .s

' is' employeto ,Y remove ammoniumcompounds: ork other.I volatile compound from they emulsions,V of

madev available;` I havefound that-when vacuum myinvention; a 'decided saving intima-.materials and manpowersisieifectedf. Also the-:photographic quality obtainablefrom theemulsion so treated is comparable to that 'obtainable by; the: washing technique-of the-priorart; Thequ'ality of the-product Vcan-.be higher esp'eciallyisincefgthere isv fno possibility 'ofi emulsionccontaminatlon: by g impurities ofiwa'sh waterfusuallyusedu.

Application December 31,1948, Serial No. 68,743r v y A s. claims. (o1. m)

The above advantages will become more apparent bycOnSide'ration'of the followingv detaileddescription" of'mylinvention.

The `nevi/"type of emulsion reactions vwhich are used involves reacting a silver compound such as silver oxide preferablyr but not necessarily dissolvedE in' an'- excess of ammonia, with an ammoniumor alkyl substitutedfammonium -halide of `the'following structure:

n .RV H" where'X isa halogen atom and R, R1 and R2 each represent a hydrogen atom, or'an alkyl group having from one to three carbon atoms, and in whichV the sum 'of the oarbon'atomsin R, Ri and its is not over three.Y

above genericv structure`V which 1 can use Avare the common amnioniumhalides, for example, arnmonium chloride,` bromide,` or iodideand Substituted ammonium halides, such as m'ethyl ammonium bromide orV chloride," dimethyl or tri# methyl ammonium halides, and ethyl ammonium bromide or chloride." I can useone or'moreof such halides together`and. particularly in` conjunction with anf ammonium iodide.v Generally, the total number of 'carbon atoms in the alkyl group or alkyl groups" attached to the nitrogenV atom in the above formulaisles's than `four because the amines of Imorec'arbon atoms resulting from the emulsion reaction, are either too insoluble to be readilyremoved by washing or 3`5' are not suiiiciently volatile tobe removed by vacuum or passing a current of air over the reaction mixture. Accordingly,l I preferto use ammonium or methyl ammonium halides in my invention.'`

The following examples are given as illustrative'of my invention:

' Example 1 Silver oxide was made in the Well-known man'-v ner bydissolving'a quantity of silver nitrate in waterand treatingwith excess sodium hydroxide solution until the silverv oxide precipitated. The precipitate was separated; and'washed by decantation.v 0.125vmol' ofthe resultant silver oxide was dissolved-inl a: l0 per cent excessofaqueous ammonia and run into a=solution containing 0.3 .mol ofammonium bromide, 0.007 mol of ammonium/iodide, lifgrams of gelatin and cc. of .water at 4,0"y C. Precautions should be taken in dissolving fthe oxide'in ammonia'due to the explosivenature lof the resultant silver complex. This may be accomplished by keeping the reaction product moist atk all times. The reaction mixture now containing silver halide, ammonia, the excess'ammonium bromide and water,was passed throughran evacuated chamber as' a thin llm of liquidati asrate'and. under a pressure such that Compounds having the only about 22 grams of ammonia remained associated with each kilogram of silver nitrate used in the reaction and converted to silver halide. The emulsion is now ready for addition of gelatin or other protein vehicle or other materials of sirnilai` property such as hydrolyzed cellulose esters or polyvinyl alcohol, and ripening or digesting operations or other steps customary in the art exclusive of washing may now be carried out.

Example 2 The silver oxide is made in the usual manner by precipitating it in a solution of aqueous silver nitrate by excess aqueous sodium hydroxide. The supernatant liquid is decanted and the precipitate is washed three times by distilled water. 0.125 mol of moist silver oxide is dissolved by 88 cc. of 28% ammonia in 100 cc. of water and the whole is diluted to 380 cc. This solution is run into a solution of 0.264 mol of ammonium bromide, 0.0053 mol of potassium or ammonium iodide and 6.1 gm. of gelatin in 380 cc. of water. The resulting mixture which contains silver halide, ammonia and excess ammonium bromide is passed through a vacuum still in which the temperature and pressure are regulated such that the emulsion emerging from the still has a pH of 8.5 or less. Gelatin is added to the emulsion, the pH is adjusted by dilute sulfuric acid and dilute silver nitrate is added and then the emulsion is finished and coated by methods customary in the art exclusive of washing.

In some cases inther examples herein, it is desirable to dissolve the silver oxide in aqueous I ammonia solution in the presence of a colloidal material such as gelatin, e. g., about 0.1% gelatin in the solution, vand in those instances when prohibitive fog results from so doing, fog may be diminished by addition of from about 0.5 to 2.5 Ing. of potassium permanganate per gram of gelatin. To the emulsion thus treated may then be added the usual emulsion addenda, gelatin, sensitizers, etc., and finished in the usual manner exclusive of washing.

Example 3 The procedure of Example 2 is followed with the exception that the ammonia used for the conversion of silver oxide is replaced by 200 cc. of approximately aqueous methylamine which yields an ammoniacal solution of the silver compound. The mixture obtained by adding this solution to the salts contains ammonia, excess ammonium bromide and methylamine. The ammonia and methylamine are removed in the vacuum still at a temperature and pressure such that the collected emulsion has a pH' of 8.5 to 9 or lower. The emulsion is then treated by the customary procedures exclusive of washing.

Example 4 Example 5 A silver salt such as silver carbonate may be employed in making my emulsions as follows:

Silver carbonate is prepared by treating an aqueous solution containing 0.25 mol of silver nitrate with excess sodium carbonate. The supernatant liquid is decanted and the precipitate is washed three times by distilled water. This is converted by adding 45 cc. of 28% ammonia and the resulting solution is diluted to 380 cc. This solution is run intoa solution of halides containing the same quantities of materials as in Example 2. The resulting mixture contains silver halide, ammonia, excess ammonium bromide and ammonium carbonate, and is passed through the vacuum still by which the ammonia and the ammonium carbonate are removed until the emerging emulsion has a pI-I of 8.5 or less. The emulsion is then treated by the customary methods exclusive of washing.

The emulsions made by the above procedures have a speed, gamma and graininess such that they are usable for fine grain negative emulsions.

Example 6 The process outlined in Example 2 is followed with the exception that the gelatin is replaced with equivalent quantities of a. water-soluble oxidized protein or protein derivative such as disclosed in the co-pending Lowe et al. U. S. patent application Serial No. 768,480, filed August 13, 1947, e. g. the acrylonitrile-acetyl derivative of oxidized casein.

In the above examples, the volatile by-prod- `ucts resulting are removed by evacuation or by passing a stream of air over the mixture. Also, it will be noted that in the above examples the silver compounds were reacted with a slight excess of halide in order that the resultant reaction mixture will contain silver halide, volatile nitrogen compound and the excess halide; however, for the purposes of my invention this excess of halide is not considered to be appreciable and the reaction mixture may be said to contain, substantially' no non-volatile Vby-product. If desired, I can, in' the above examples employ equivalent amounts of silver and halide compounds and produce useful emulsions in the manner of my invention.

The peptizing lyophilic colloids which I use during the step of precipitating the silver halide, are materials such as gelatin, polyacrylamide or imide resins such as disclosed in Lowe et al. U. S. application, Serial No. 685,375, iiled July 22, 1946, now Patent No. 2,541,474; casein, modified proteins such as disclosed in Lowe etal. S. application, Serial No. 768,480, filed August 13, 1947, and similar materials. Y

In order to remove the ammonia from the emulsion systems I describe, I have found it advisable to supply heat to the liquid being evacuated to compensate for the drop in temperature arising from the heat supplied for vaporization and the tendency for the rate of removal of ammonia to fall with drop in temperature thereby. The rate and extent of the removal of moist ammonia is, of course, controlled on the one hand by the peculiarities of the vacuum equipment and the flow of the liquid through it which naturally depends in some degree upon the capacity of the `vacuum pumping means. A useful range of 5 operation.V includesi a; range;` of pressi'iireq the. vacuum system oigfrom 20Jtoi30'mm. ofmercury; ori4 lowerl'andiawheniheatiis suppli'edlftothelliquid lmlby v'means ofi alwater jacketLafLran'get-o ltem"- perature.l from:.60lto80' Cf. .inthel'jacket-.is satis'- factory'. Howevenl. a Itypical1.alli-glass installation using water jacketsfand: aspiratorfpnmps; appreciable amounts.: oi` ammonia'l. arel removedl withthe Wate11Jaif140 C. andL-ava'cuum;pressureof 901mm; As'vis' apparent', thenio'stfsuitable'or desirable conditions? off rate-fot now, `temperature and: pressure; fori al. given, apparatusiv areireadilydeter-minables. butl depend: on definite'. character'- istics of that equipment. lAfter I determine-1 the: characteristics of the vacuumsystem, that is, its rate of 'removal of Iammonia or dissolved material, I am next governed by matters of economy and v'phi'ltographiviz quality. That is, in Vcertain" inand .time of.v thef ammoniasolutions incontactv with they silver salt; it Yis'desirabl'lto operate my inventioniin such avi-aythat'the grains-of silver salt are ripened and the ammoniagis reduced'in concentration to less than 22 grams per kilogram of silver nitrate convertedto silver halide in a total time of less than 2 hours. ThisI may accomplish either by short ripening and slow removal or'by'more .prolonged ripening and fast removal or short ripening and fast removal.

One advantage of my process is now apparent. Having determined the operating characteristics of the emulsion making system I may remove practically any quantity of ammonia or volatile material from the silver halide reaction mixture.

If'I desire an emulsion lhaving all of the characteristics derivable from a similar well-Washed emulsion, I remove that amount of ammonia which corresponds to Washing. Similarly, if desired, I remove less ammonia with the result,

among other things, ofv obtaining an appreciable.`

increase in theoutput of the evacuation system'. Since vsensitometric characteristics and photographic quality are of prime importance, I remove an amount of ammonia commensurate with utmost economy and proven dictates of photographic quality.

Finished lemulsions having desirable photographic qualities can be made by removing ammonia until a range of from about 0 to 22 grams of ammoniaper kilogram of' silver nitrate (5.9

according-'to2 Example-14,.; theieilciency'f of my: 'n

processzmaybe lowered kprincipally because oitlie higher boilingvv pointA ofF th'efi aliphatic: aminev formed in the reaction andwhi'ch is to be. removed from the reaction mixture. Int suchcases I may` desire to' Washl the.. material fromA- the'.- emulsion with. or. Without J previousv evacuation. treatment:

` adaptable. i to. removing; theammonias justy afterl or.` 'as soonz atter'for.rnation, of silver: halide a'sfis possiblefxandK thereforeimay. be readily-fadapted:l to?` a continu'ousmanufacturing processi.. L merely? conduct,.the=i silfven'y halide reaction; mixture?- continuous vmanner Vfromtheereactior-rv chamberrto thev evacuation chamber-:andi the f evacuation Y systemis operatedat: a'. fairly 'lovv-'capacityzg .Iiu'se` afftemporary holding; tank; therebetween; An. aclvantage ofi the: quick; removali` of; ammoniasf` `on amine jlies inl the?y fact that; .the` emulsionuhzazs:V no,` vappreciabl'ef` opportunity' tosripenlfin.,therpresence or;anun'desirablerquantityeor ammoniaor amine; and it; is-re'movedmuch moreyquickly; thanibyi `Washing; Thereforegzsi'lver fhali'de grainsize'cany t ybe controlled more readily thanfprevouslyyby operatingaccording to myrinventiom.

' It is to'be: noted'. th'ati: when the, composit'izm-r vresulting. fromA my f process issripenedr; ori` digested or.' treatedfas' usual; thefnishedl-Y emulsionsha's; as f good characteristicsasl ittrvvould?havezslrad, had

.. period prior to and including Washing.

It is to be understood that the disclosure herein is by Way of example andI consider las includedl in my invention all modications and mols of silver nitrate or 2.95 mols calculated as v silver oxide or silver carbonate) used in making the emulsion and converted to silver halide remains associated with the silver halide. That is, the volatile nitrogen compounds present in the reaction mixture are removed until the molecular equivalent of the nitrogen compound remaining in the emulsion is equal to less than about 22 grams of ammonia per kilogram of silver .nitrate used.

It Will be apparent that Whenan alkyl substituted ammonium halide is used, for example,

equivalents falling Within the scope of the ap pended claims.

What I claim is:

1. Amethod of making a photographic silver halide emulsion which comprises reacting in an excess of aqueous ammoniacal solution substantially free of nitrate ion in the presence of a peptizing hydrophilic colloid for silver halide, substantially equivalent molar quantities or fa compound selected from the group consisting of silver oxide and silver carbonate with at least one of the amine halides having the formula R1;l\I X y R2 l H Y y wherein X represents a halogen atom, R., Ri and R2 each represents a member selected from the group consisting of a hydrogen atom and an alkyl group having from 1 to 3 carbon atoms, the

sum total of the carbon atoms in R, R1 and Rz being from 0 to 3, to yield a silver halide emulsion containing silver halide, a Volatile nitrogen compound and substantially no other non-volatile product, removing said volatile nitrogen compound from said emulsion only by passing the emulsion as a thin film of liquid through a chamf Aber maintained at apressure of from about 20-90 mm. of mercury anda temperature offrom about iO-80 C. until the molecular equivalent amount of thenitrogen compound remaining in the emulsionis equal to less than about 22 grams of arnmonia per 2.95 mols oi, said silver compound selected from the group consisting Aof silver oxide andsilver carbonate used in making the emulsion and .converted to silver halide, and digesting the emulsion, the removal of nitrogen compound and digestion being effected Within less than two hours.v

- 2. A method of makinga photographic silver halide emulsion which comprises reactingin excess aqueous ammonia solution substantially free of nitrate ion in the presence of gelatin, substantially equivalent molar quantities of silver oxide and an ammonium halide to yield a silver halide emulsion containing Vsilver halide, ammonia and substantially no other non-volatile product, removing the ammonia from the emulsion only by passing the emulsion as a thin film of liquid through a chamber' maintained at a pressure of from about 20 to 90 mm. of mercury and a temperature of from about 40-809 C. until the amount ofammonia remaining in the emulsion is equal to less than about 22 grams of ammonia per 2.95 mols of silver oxide used in making the emulsion and converted to silver halide, and digesting the emulsion, the removal of ammonia and digestiony being effected Within less than two hours.

3. A method of making a photographic silver halide emulsion which comprises reacting in eX- cess aqueous ammonia solution substantially free of nitrate ion `in the presence of gelatin, substantially equivalent molar quantities of silver carbonate and an ammonium halide to yield a silver halide emulsion containing silver halide, am: monia and substantially no other non-volatile product, removing ,the ammonia from the emulsion only by passing the emulsion as a thin lm of liquid through'a chamber maintained at a pressure of from about 20 to 90 vmm. of mercury and a temperature of from about 40-80 C. until the amount of ammonia remaining in the emulsion is equal to less than about 22 grams of ammonia per 2.95 mols of silver carbonate used in making the'emulsion and converted to silver halide, and digesting the emulsion, the removal of ammonia and digestion being effected Within less than two hours.

RUDOLPH E. DAMSCHRODER.

References Cites in, the me of this patentA UNITED STATES PATENTS OTHER REFERENCES -Wall, Photographic Emulsions, published by American Photographic Publishing Co., 1929, pp. 221, 222, 223, 225 and 226 cited, pp. 158-7161.

`The Amateur Photographer, vol. 18, pp. 223, 224, 242, and 243. 

1. A METHOD OF MAKING A PHOTOGRAPHIC SILVER HALIDE EMULSION WHICH COMPRISES REACTING IN AN EXCESS OF AQUEOUS AMMONIACAL SOLUTION SUBSTANTIALLY FREE OF NITRATE ION IN THE PRESENCE OF A PEPTIZING HYDROPHILIC COLLOID FOR SILVER HALIDE, SUBSTANTIALLY EQUIVALENT MOLAR QUANTITIES OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF SILVER OXIDE AND SILVER CARBONATE WITH AT LEAST ONE OF THE AMINE HALIDES HAVING THE FORMULA 